The present invention relates to a method of manufacturing armatures of electric rotary machines.
Referring to FIGS. 7 through 9, a conventional armature of an electric rotary machine will be described. FIG. 7 is a partly omitted front view showing a main part of a specific typical example of the conventional armature used in a starting motor, FIG. 8 is a sectional view along the line VIII--VIII in FIG. 7, and FIG. 9 is a sectional view along the line IX--IX in FIG. 7. In the drawings, the armature is constituted by a shaft 20, an armature core 21 having slots formed in its outer circumference, a commutator body (an annular resin body) 22, commutator segments 23, and pairs of armature coils 24 and 25 wound in the respective slots of the armature core 21. The armature having the foregoing constituent components is manufactured through the following process. The armature core 21 is pressed onto the shaft 20, a pair of the armature coils 24 and 25 are wound in each of the slots of the armature core 21, and the commutator body 22 prepared in advance in the separate step is pressed onto the shaft 20. The armature coil 24 inserted in each slot of the armature core 21 is bent circumferentially by a predetermined angle so as to form a lower lead-out portion 24A and the other armature coil 25 in each slot is also bent but in the reverse direction by a predetermined angle so as to form a lead-out portion 25A as shown in FIG. 7. One of the thus bent lower lead-out portions 24A of the armature coil 24 in one slot is paired with one of the upper lead-out portions 25A of the armature coil 25 in another different slot and each pair of lower and upper lead-out portions 24A and 25A are inserted at their ends into corresponding one of number of riser grooves 27 formed in the circumference of a riser portion 26, and then fastened and welded so as to be mechanically and electrically joined to corresponding one of the commutator segments 23 of the commutator body 22 in the riser groove 27. An end coil insulator 28 is interposed between each pair of the lower and upper lead-out portions 24A and 25A. The process of manufacturing such a conventional armature requires a number of manufacturing steps, troublesome work for arranging riser grooves in the commutator body and for carefully joining the armature coils to the respective commutator segments in the riser grooves, and provision of expensive commutator segments. Accordingly, the armature becomes expensive.
Recently, therefore, there has been proposed an armature manufacturing method in which one of each pair of lead-out portions of armature coils is embedded in corresponding one of grooves of an annular resin body constituting a commutator body by means of pressure fitting of the like, and the other lead-out portion of the pair is welded with the one lead-out portion so that an outer periphery of either one of the one and the other lead-out portions of the pair can slidably contact with a power feeding brush to thereby make a part of the lead-out portion serve also as a commutator segment, as disclosed in JP-A No. 56-132147, etc.
The aforementioned armature manufacturing method in which one of each pair of lead-out portions the armature coils is used also as a commutator segment, has an advantage in that expensive commutator segments which have been prepared in a separate step become unnecessary and the joining work between armature coils and commutator segments requiring troublesome and careful working can be eliminated, however, has the following problems to be solved.
In the conventional armature manufacturing method in which one of each pair of the lead-out portions of the armature coils is used also as a commutator segment, one of the coil lead-out portion in the pair is embedded in one of the corresponding one of the groove portions of the commutator and welded with the other lead-out portion in the pair in the groove. In such a coil lead-out portion fixing structure has a limit in mechanical strength against centrifugal force in high speed rotation of the armature, so that there is a possibility that the coil lead-out portions come off by the centrifugal force due to high speed rotation. Accordingly, the method could be put into practical use only for relatively low speed electric rotary machines. Particularly in the case where high speed rotation, for example, about 30,000 rpm, is required, for example, in starting operation of a starting motor provided with a reduction gear, the aforementioned armature manufacturing method has been difficult to be put into practical use because the armature manufactured by the method can not have sufficient mechanical strength against rotation.